Once you have all your tracks done, all your MIDI converted to audio (if you use MIDI), everything mixed and all your levels sounding the way you want, you have to mix it all down and export it as a 2-track stereo file. Then you open it in a wave editor like Sound Forge or Wave Lab, and that's where you would apply the Ozone or any other mastering plugins you want to use. Individual tracks normally have FX applied before final mix. For example, you may want to add compression, reverb, and EQ to your guitar tracks individually, making sure they sit in the mix nicely, then export the whole thing to 2-track. Do your mastering from that point. The main reason is that it's rare that a single reverb will compliment all the tracks in a mix. Same with EQ. You're not gonna find a single setting that enhances the drums, bass, and keyboards all at the same time while bringing the vocals out front as well. I know I'm being long-winded here, and I apologize. Bottom line: Mix all your tracks down first; export a 2-track audio file; then mess with your Ozone. Hope this helps a bit.
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